Abstract: A 1.5 .mu.m zero dispersion single mode optical fiber comprising a center core, a side core disposed on an outer side of the center core and having a refractive index lower than that of the center core, and a cladding portion disposed on an outer side of the side core. Each of the refractive indices of the center core and the side core has a step-like profile in the direction of the radius of the optical fiber. The bending loss is low. The mode field diameter can be increased without deteriorating the bending loss, and the splice loss can be reduced. The chromatic dispersion varies only to a small extent with respect to changes in the core diameter, so that the zero dispersion wavelength can be well controlled.

Abstract: A reinforced glass fiber for use in optical transmission comprising an optical fiber coated with (1) a coating of a first curable organopolysiloxane composition having a refractive index higher than that of the clad glass which forms the outermost layer of the optical fiber, said first curable organopolysiloxane composition being baked, (2) a coating of a second curable organopolysiloxane composition which can be the same as or different from the first curable organopolysiloxane composition, the second curable organopolysiloxane composition being provided on the first curable organopolysiloxane composition and being baked, and (3) optionally a coating of a thermoplastic resin composition.